Bolometric measurement of the charge-density-wave gap in TaS3

Polarized bolometric spectra were measured on orthorhombic Ta${\mathrm{S}}_3$ between 20 and 100 K. At the lowest temperature, the spectra are clearly absorption spectra, indicating that $o-\mathrm{Ta}{\mathrm{S}}_3$ has a semiconducting Peierls gap of $E_g=1240\mathrm{} {\mathrm{cm}}^{-1\mathrm{}}=8.1\mathrm{}{k}_B{T}_c$. No sharp lines indicative of midgap soliton states are observed, although a long tail may be due to weakly pinning impurity states. The spectra become more complex at higher temperatures, but indicate that the gap decreases to 1025 ${\mathrm{cm}}^{-1\mathrm{}}$ at 95 K. The gap energy is close to twice the activation energy observed in transport measurements.